It is well known that living polymerization (i.e., polymerization proceeding in the practical absence of chain transfer and termination) is a very useful method for designing polymer structures, permitting for example, control of the molecular weight and molecular weight distribution of the polymer, as well as enabling functional groups to be positioned at desired points in the polymer chain. Since Szwarc et al. demonstrated the living nature of polystyryllithium formed from the reaction of sodium naphthalene and styrene in the 1950s, a wide variety of living polymerization schemes have been developed, including cationic, anionic, radical, ring-opening, and group transfer polymerization.
Copolymers are an important class of polymers and have numerous commercial applications. For instance, their unique properties, whether in pure form, in blends, in melts, in solutions, and so forth, lead to their use in a wide range of products, for example, compatiblilizers, adhesives and dispersants. An advantage of combining various polymerization techniques (e.g., cationic and anionic polymerization techniques in the case of the present invention) is that new copolymers, each with its own unique properties, can be prepared which could not otherwise be prepared using a single polymerization method.
For example, polyisoolefins are attractive materials because the polymer chain is fully saturated and, consequently, the thermal and oxidative stability of this polymer are excellent. Polyisoolefins are prepared by cationic polymerization. Recently, Muller et al. reported that poly(alkyl methacrylate)-b-polyisobutylene and poly(alkyl methacrylate)-b-polyisobutylene-b-poly(alkyl methacrylate) copolymers can be prepared by the combination of cationic and anionic polymerization techniques. See Feldthusen, J.; Iván, B.; Müller, A. H. E. Macromolecules, 1997, 30, 6989-6993; Feldthusen, J.; Iván, B.; Müller, A. H. E. Macromolecules 1998, 31, 578-585. In this process, an end-functionalized polyisobutylene (PIB), specifically 1,1-diphenyl-1-methoxy end-functionalized polyisobutylene,
or 2,2-diphenylvinyl end-functionalized polyisobutylene,
is prepared by the reaction of living polyisobutylene with 1,1-diphenylethylene. The chain end of the resulting polymer is subsequently metallated with alkali metal compounds such as sodium/potassium alloy or cesium in tetrahydrofuran at room temperature. The thus produced macroanion is capable of polymerizing monomer. This method, however, is inconvenient because of the complicated process for the metallation of the polymer chain using alkali metal compounds.
A more recent attempt to combine cationic and anionic polymerization techniques involves the preparation of end-functionalized polymers (e.g., end-functionalized polyisobutylene) by reacting a carbocationically terminated polymer with a heterocyclic compound (e.g., thiophene) to provide an end-capped polymer (e.g., thiophene end-functionalized polyisobutylene). The end-capped polymer is then reacted with an organolithium compound to yield an anionically terminated polymer, which is subsequently reacted with an anionically polymerizable monomer such as tert-butyl methacrylate to produce a copolymer. See, Application Ser. No. 60/480,121 filed Jun. 20, 2003 and entitled “End-Capped Polymer Chains and Products Thereof”, and Martinez-Castro, N,; Lanzendo1fer, M. G.; Muller, A. H. E.; Cho, J. C.; Acar, M. H.; and Faust, R. Macromolecules 2003, 36, 6985-6994. An advantage of this process is that simple and complete metallation is achieved. This process, however, is also subject to improvement. For example, in the case where thiophene end-functionalized polyisobutylene is formed, to prevent coupling between thiophene functionalized polyisobutylene and living polyisobutylene, an excess of thiophene is used while functionalizing the polyisobutylene cation with the thiophene. Moreover, the blocking efficiency was found to be only about 80% even when a low molecular weight product is targeted.